This invention relates to a system and method for operating electric power systems and more particularly to a system and method utilizing optimal power flow (OPF) with transient stability constraints taken into consideration.
It is more strongly demanded than before to further enhance the operation efficiency of the electric power system and lower the operation cost due to drastic changes of environment for electric power industries in recent years, for example, deregulation or liberalization of electric power markets in Europe, Japan and United States of America. However, as is well known in the art, generally economics and stability have a trade-off relation for operation of power systems. In other words, if only the economical efficiency is considered in preference to other factors, the stability constraints may not be satisfied in the operation. If an operation solution which makes the operating cost (for example, fuel cost for turbine boilers) minimum can be determined by satisfying all of the operating conditions including the stability constraints of the system, it becomes possible not only to lower the operating cost but also to maintain the stability constraints.
In many deregulated electric power markets, e.g., in U.S.A., the evaluation of the available transfer capability (ATC) is mandatorily required, but dynamic constraints such as the transient stability constraints are still unable to be taken into consideration in ATC calculation due to theoretical and practical difficulties of computation. Therefore, it is imperatively required to rapidly develop a calculation method for ATC which takes the transient stability constraints into consideration in electric power industry. If a computational technique for OPF with the transient stability constraints can be developed, ATC with the transient stability constraints can be evaluated by solving a problem which maximizes transmission electric power between two points subject to transient stability constraints together with conventional operational constraints.
As mentioned above, ATC calculation is conventionally carried out mainly by taking only the static constraints (such as upper and lower bounds of power flow in the power transmission line or the like) of the electric power transmission network, but it is considered necessary to take the stability into consideration from the viewpoint of the security of the system. If ATC with the stability constraints taken into consideration can be calculated, then the above problem can be solved.
As one of the most important indices to evaluate the stability of the electric power system, the transient stability indicates the degree to which the stable synchronized operation of a synchronous generator can be maintained during and after the time of occurrence of disturbance in the power system. In practice, the practical power system is operated on the assumption that the transient stability is maintained even if a single equipment breaks down. Further, to protect the system from some rare cases of breakdowns such as cut-off of the route in the power transmission network, a system stabilizing relay for maintaining the transient stability of the whole system by tripping a pumping-up generator or limiting the power of a power supply has been put into practical use.
An optimal power flow method is conventionally proposed as a method for determining the optimal operation solution of the electric power system and is used for the planning and operation. However, it is considered difficult to take the transient stability into consideration in the optimal power flow calculation. Therefore, in principle, it is possible that an operation solution obtained by the conventional OPF without consideration of transient stability may not satisfy transient stability constraints.
In such a case, it is necessary for the system operator (or independent system operator) to make the adjustment of load dispatch again and modify the operation solution so as to satisfy the transient stability.
The modification process is traditionally implemented by heuristic trial-and-error methods based on engineering experience and judgment, which not only may sacrifice the optimality but also are time-consuming and not suitable for automated computation.
An object of this invention is to provide a system and method for operating electric power systems and utilizing an optimal power flow calculating method with transient stability constraints incorporated therein.
In order to attain the above object, this invention provides an available transfer capability calculating system in the operation of an electric power system for calculating optimal power flow for assumption failures (or contingencies or accidents) occurring in the electric power system and deriving the available transfer capability of the electric power system based on the calculated value of the optimal power flow, comprising an optimal power flow calculating processor for deriving data relating to a maximum electric power value and an initial phase angle of a generator by calculating mechanical output and electrical output of the generator containing a generator phase angle defined by a time function in a condition that the generator phase angle does not exceed a preset value; a data collecting section for collecting system configuration data of the electric power system for effecting the calculation of the optimal power flow calculating processor; a data input section for inputting failure condition data and constraint data used for effecting the calculation of the optimal power flow calculating processor; and an output section for outputting data relating to the maximum electric power and phase angle of the generator derived by the optimal power flow calculating processor.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.